Biological and physicochemical factors controlling short-term variability in phytoplankton primary production and photosynthetic parameters in a macrotidal ecosystem (eastern English Channel)

Links between short-term variability of phytoplankton primary production and community structure changes have been studied rarely. This has been examined in a macrotidal ecosystem, the Baie des Veys (eastern English Channel, France), in 2003 and 2004, over the complete tidal cycle (semi-diurnal mode, 12 h). Within this area, primary production and photosynthetic parameter estimates, according to the 14C incorporation technique, were supported by an exhaustive taxonomic study and measurements of physicochemical factors to illustrate the environmental framework. Related to the river Vire discharge, daily interactions between estuarine and bay waters were demonstrated. Depth-integrated primary production P z was maximal around noon in the bay (48.7–68.0 mg C m −2 h −1) and decreased through the day in the mouth of the river. Photosynthetic parameters' variations and photoacclimation were influenced by the ecosystem variability level: short-term photoacclimation was possible in low mixing conditions. Changes in taxonomic composition according to tidal forcing led to variations in primary production levels. Large species, associated with high photosynthetic parameters, were observed in the bay, whereas small ones were present in the mouth of the river, when low primary production was measured. On a short-time scale, a positive relationship was observed between species diversity and primary production. This work emphasizes the need to focus on changes in phytoplankton community structure in order to understand short-term variability in primary production.